1. Field of the Invention
The present invention relates to the fabrication of semiconductor light-emitting devices. More specifically, the present invention relates to a method for fabricating semiconductor multi-quantum-well (MQW) light-emitting device on a “single-crystal sacrificial layer/base substrate” type of combined substrate and transferring the light-emitting film to a support substrate.
2. Related Art
InGaAlN semiconductor light-emitting devices (LEDs) have been widely used in many applications, such as large screen-displays, traffic lights, backlight sources for display, illuminations, and so on. Traditionally, InGaAlN materials have been epitaxially grown on a sapphire substrate and are generally made into light-emitting devices with lateral-electrode configurations. Such devices often suffer from low efficiency and poor heat-sinking capability. In addition, the p-type conductive layer in such devices often absorbs light, thereby impairing the performance of light-emitting devices.
LEDs with a vertical electrode configuration often have better performance and improved reliability. To fabricate a vertical-electrode LED, it is possible to use laser-liftoff (LLO) and wafer-bonding techniques to transfer an InGaAlN film epitaxially grown on a sapphire substrate to a support substrate with a better thermal conductivity. However, the laser used in the LLO equipment is often expensive, and the LLO process is difficult to control. Consequently, it is difficult to achieve large-scale, cost-efficient production of vertical-electrode LEDs using the LLO technique.
Si substrates cost less and are easy to produce. It is economical to grow an InGaAlN epitaxial film on a Si substrate, and then use wet-etching and wafer-bonding techniques to transfer the InGaAlN epitaxial film to a support substrate and to fabricate a vertical-electrode LED. Such an approach can improve the light-emitting efficiency and lower the serial resistance of the LED. However, there remains a significant mismatch of thermal expansion constant between the Si substrate and InGaAlN film, which may lead to cracking of the InGaAlN structure during the epitaxial growth process. It has been shown that pre-patterning the Si substrate with grooves and mesas can reduce such stress and solve the cracking problem of InGaAlN film. However, the pre-patterning process and subsequent device fabrication is often complex. Furthermore, the large thermal-expansion-constant mismatch may lead to bending and deformation of the epitaxial film.
The bending and deformation of the epitaxial film can significantly impact the uniformity of the fabricated device and introduce difficulties into the fabrication process. For example, the growth temperature of the InGaN quantum well is lower than that of the n-type layer and the buffer layer; therefore, after the growth of the n-type layer and during the growth of the quantum well, the epitaxial film can be slightly bent. This bending directly affects the uniformity of the surface temperature field on the epitaxial film, thus affecting the uniformity of the quantum well, which in turn impairs the uniformity of key parameters such as emission wavelength and operation voltage. In addition, a severely bent and deformed epitaxial film will make subsequent wafer bonding difficult.